Background: The aim of this study was to test the prognostic value of day 3 LH in predicting the success of ovarian response in patients with polycystic ovary syndrome. Methods: A prospective observational study was conducted at Infertility outpatient clinic, Cairo University Maternity Hospital .Patients were sixity PCOS women who underwent induction of ovulation. All women had serum basal LH measured before induction of ovulation. The main outcome measured was ovarian response using folliculometry and serum progesterone. Results: PCOS women with LH < 8 mIU/ml had higher incidence of ovulation than those with LH>8 mIU/ml using both folliculometry and serum progesterone (44.73% vs 10.52% ,P=0.01 ) , also PCOS women with LH/FSH ratio <2 had higher incidence of ovulation than those with LH/FSH ratio>2 (40.9 % vs 7.69 %, P=0.026). Conclusions: Basal serum LH and LH/FSH ratio may has useful prognostic value in the prediction of ovarian response in patients with PCOS.